Magnetic sensors are used for a variety of applications to sense motion, position, vibration, speed and the like. Such sensors are often used in motor vehicles and marine crafts. In both cases, the sensors are often required to operate in ambient conditions which may be deleterious to sensor components. Examples of such ambient conditions include exposure to high humidity, salt water spray, corrosive fluids or fumes, temperature extremes and the like.
U.S. Pat. No. 5,416,410 to Kastler and U.S. Pat. No. 5,563,511 to Van Fleet disclose magnetic sensors with protective caps. However, in both devices the caps are formed of a magnetically impermeable, or non-magnetic, material, the use of which may interfere with operation of the sensor. Moreover, the Kastler design does not account for possible dimensional variations in sensor components due to thermal cycling. As such, leaks may develop, leading to corrosion and eventual failure of the sensor.
U.S. Pat. No. 5,486,758 to Hammerle and U.S. Pat. No. 5,585,560 to Goossens also disclose sensors having protective caps. The caps in these two prior art devices are formed from non-magnetic stainless steel, which may cause interference with sensor readings. Moreover, the two prior art designs require the use of sealing elements or o-rings in addition to the protective cap, making these designs more costly to produce.
U.S. Pat. No. 5,563,510 to Gorrell et al. and U.S. Pat. No. 5,629,618 to Babin et al. disclose sensor housings. In Gorrell et al. the sensor housing is of unitary construction and is manufactured from a polyether-imide. Similarly, the housing disclosed in Babin et al. is formed of an injection molded plastic which is overmolded after the sensor is assembled. Such designs are undesirable because, as is well known in the art, plastic housings, such as those disclosed in these two prior art devices, deleteriously affect performance of the sensor.
Finally, U.S. Pat. No. 4,797,612 to Nakanishi et al. discloses a speed detector having a removable covering to protect the inner components of the detector. The covering has a cylindrical wall which is provided with a lip extending radially outward. The lip is held in "abutting contact" with the steering knuckle of the vehicle. However, no provision is made for thermal cycling, and the area of "abutting contact" is particularly prone to leaking.
What is desired, therefore, is a magnetic sensor having a sealing cap which protects the sensor from ambient conditions that may be deleterious to sensor components without interfering with sensor performance.